[esp8266] Add enable_scanf_float option (#15284)

tests/components/esp8266/test.esp8266-ard.yaml

@@ -14,3 +14,6 @@ esphome:
         assert(x == 95);
         x = clamp_at_most(x, 40);
         assert(x == 40);
+    - lambda: |-
+        float value = 0.0f;
+        sscanf("3.14", "%f", &value);

tests/unit_tests/components/test_esp8266.py

@@ -0,0 +1,62 @@
+"""Tests for ESP8266 component."""
+
+import pytest
+
+from esphome.components.esp8266 import lambdas_use_scanf_float
+from esphome.core import Lambda
+from esphome.types import ConfigType
+
+
+@pytest.mark.parametrize(
+    ("src", "expected"),
+    [
+        # Basic float formats
+        ('sscanf(buf, "%f", &v)', True),
+        ('sscanf(buf, "%F", &v)', True),
+        ('sscanf(buf, "%e", &v)', True),
+        ('sscanf(buf, "%E", &v)', True),
+        ('sscanf(buf, "%g", &v)', True),
+        ('sscanf(buf, "%G", &v)', True),
+        ('sscanf(buf, "%a", &v)', True),
+        ('sscanf(buf, "%A", &v)', True),
+        # With modifiers
+        ('sscanf(buf, "%lf", &v)', True),
+        ('sscanf(buf, "%Lf", &v)', True),
+        ('sscanf(buf, "%8lf", &v)', True),
+        ('sscanf(buf, "%*f")', True),
+        ('sscanf(buf, "%.2f", &v)', True),
+        # Mixed formats
+        ('sscanf(buf, "%d,%f", &a, &b)', True),
+        # fscanf and std::sscanf
+        ('fscanf(fp, "%f", &v)', True),
+        ('std::sscanf(buf, "%f", &v)', True),
+        # Multi-line
+        ('sscanf(buf,\n"%f", &v)', True),
+        # No float format
+        ('sscanf(buf, "%d", &v)', False),
+        ('sscanf(buf, "%s", s)', False),
+        # printf not scanf
+        ('printf("%f", val)', False),
+        # %f in a different statement after scanf
+        ('sscanf(buf, "%d", &x); printf("%f", val);', False),
+        # scanf %f in comment only
+        ('// sscanf(buf, "%f", &v)\nsscanf(buf, "%d", &x)', False),
+        ('/* sscanf(buf, "%f") */\nsscanf(buf, "%d", &x)', False),
+    ],
+)
+def test_lambdas_use_scanf_float(src: str, expected: bool) -> None:
+    """Test scanf float detection in lambda source."""
+    config: ConfigType = {"test": [Lambda(src)]}
+    assert lambdas_use_scanf_float(config) is expected
+
+
+def test_lambdas_use_scanf_float_no_lambdas() -> None:
+    """Test with config containing no lambdas."""
+    config: ConfigType = {"key": "value", "list": [1, 2]}
+    assert lambdas_use_scanf_float(config) is False
+
+
+def test_lambdas_use_scanf_float_nested() -> None:
+    """Test detection in deeply nested config."""
+    config: ConfigType = {"a": {"b": {"c": [Lambda('sscanf(buf, "%f", &v)')]}}}
+    assert lambdas_use_scanf_float(config) is True